Our immediate research objectives comprise different but parallel approaches to the understanding of infection with influenza viruses. Primary objectives during the past year have included: (1) detailed genetic and antigenic analysis of coexisting variants of recently isolated swine influenza viruses; (2) investigations in a mouse model system of cellular immunity to influenza virus infection; (3) genetic analysis of influenza virus virulence and (4) study of influenza RNA synthesis. The nature of viral dimorphism will be further investigated by amino acid sequencing of cyanogen bromide fragments of the isolated hemagglutinin proteins of dimorphic variants. We plan also to characterize in an in vitro system the functions of internal proteins of influenza virus known to participate in vRNA synthesis. Our studies of cellular immunity will be focused on the role of cross-reactive T-cell responses in resistance to infection and particularly in heterotypic immunity.